50mm F/1.8 & +4 closeup filter question

Hi guys,

Anyone tried to add a +4 closeup filter on a nifty fifty? What to expect from this setup, macro-wise? Would it allow me to get a better magnification than my EFS 55-250 (which is about x0.31)? I probably don't need x1 magnification, but half that would be nice.

That'd be to shoot small objects in my house (coins, watch, etc.) and flowers too. Not interested in insect photography.

Any sample picture would be great. I've found one so far (http://i18.photobucket​.com …DiT77/forums/DS​C_1579.jpg) and it looks really good.

I'm on tight budget, so a dedicated macro lens is a no go. I find extension tubes pricey as well.

I'm aware that a closeup filter will impact on IQ, but that may not be noticeable enough to be an issue. Any hand on experience with such filters would then be very welcome.

Thanks!

A +4 closeup lens is not a filter in the true sense , it is really a screw-on lens. A very good one is the the Canon 250D, which is a two-element, achromatic version of such a lens.

A close-up lens will add some additional magnification to the magnification the lens it is mounted to already offers. The additional magnification is equivalent to FL_lens/FL_closeup_len​s.

Since a 4 diopter closeup lens has an FL of 250 mm (1000 mm / 4), this means that at 50 mm you get an additional 0.2X magnification, and at 250 mm and additional 1X magnification. This, BTW, is the minimum magnification you will get with such a lens mounted to your lens, and hence you won't be able to focus to infinity anymore until you take it off again. The maximum magnification you will now get you can calculate by adding this magnification to the maximum magnification the lens alreay offers.

So, the new maximum magnification at 250 mm will be 0.31X + 1.0X = 1.31 X. But then, the minimum magnification will be 1.0X. IOW, the reach (and therefore the related focusing distance) will be from 1.0X to 1.31X magnification. You can calculate the focusing distances for this too, but I currently don't have the lens formula at hand; I don't use it that often. At 55 mm it will be at least 55/250=0.22X, the maximum whatever it has for magnification at 55 mm, plus an additional 0.22X.

IOW, what you really want to do is change magnification by zooming.

BTW 4 diopters is a bit much for use with 250 mm of FL; you may introduce quite a few aberrations. Personally, I would go no higher than 3 diopters or thereabouts with a 250 mm FL.

HTH, kind regards, Wim

Thanks for the explanation Wimg, that's very useful.

If I understand correctly, a +4 closeup lens on my nifty fifty would not make much sense since my 55-250 can already reach that level of magnification.

Nifty + closeup lens: x0.15 + x0.2 = x0.35
Stock 55-250 at 250mm: x0.31
55-250 at 250mm + closeup lens: x0.31 + x1 = 1.31

Does the closeup lenses reduce minimum working distance the same way as extension tubes do? My main issue with the nifty fifty is that the closest focus distance is at 0.45m. If I could get it down to 0.15-0.20m that would be awesome. Looking through the viewfinder at that distance gives me a nice magnification, but then it's obviously all blur hehe.

Any math formula to calculate the new minimum focus distance?

Thanks!

cedm wrote in post #6521226
Thanks for the explanation Wimg, that's very useful.

If I understand correctly, a +4 closeup lens on my nifty fifty would not make much sense since my 55-250 can already reach that level of magnification.

Nifty + closeup lens: x0.15 + x0.2 = x0.35
Stock 55-250 at 250mm: x0.31
55-250 at 250mm + closeup lens: x0.31 + x1 = 1.31

You do understand correctly .

No, not entirely. essentially you change the total FL of the system, i.e., the FL of the lens used and the FL of the closeup lens together form a new lens system with a different focal length, and hence different WD dynamics.

Yes, there is, but I need to look it up. No chance or time yet. I could derive it, but that takes a bit more time, my optical formula knowledge is a bit rusty .

In the mean time, here is a table that will help:
http://www.bobatkins.c​om …graphy/eosfaq/c​loseup.htm

A few more links:
http://www.naturephoto​graphers.net/articles1​202/th1202-1.html
Just scroll down a bit for some info on the Canon 500D closeup lens.

http://www.camerahobby​.com/Access-Canon500D.htm
Interesting read on the 500D.

Later more (I hope).

Kind regards, Wim

Ah, I remembered again.

There are two ways to go about calculating the FL of the total system, i.e., closeup lens and lens it is mounted to.

You can either work with diopters, or with actual focal lengths:

FL_system = 1000/(closeup_lens_dio​pters + main_lens_diopters)

and your main lens diopters you can calculate by using:

main_lens_diopters = (1000 / FL_main_lens)

The second method, working with actual focal lengths, is to convert the diopter value of the closeup lens to an FL, and then use the following lens formula:

1/FL_System = 1/FL_main_lens + 1/FL_closeup_lens

And the FL of the closeup lens can be calculated by using the diopter conversion formula:

FL_closeup_lens = 1000/closeup_lens_diop​ters, in mm of course.

Once you have the system's FL, you can now go about calculating the minimum and maximum focusing distances, and you need the magnification factors for this as well.

magnification = image_of_object_size / object_size = image_distance_to_rear​_nodal_plane / object_distance_to_fro​nt_nodal plane

The latter two combined give a good indication of the total distance from sensor plane to object, provided the nodal planes of the lens aren't too far apart.

To calculate these distances, you have to do a few substitutions in the lens formula:

1/FL_system = 1/image_distance + 1/object_distance
Note: I left the nodal plane bits out for brevity

If you substitute the magnification factor in this formula, and work things out, you'll get:

image_distance = FL_system * (magnification +1)
and
object_distance = magnification * image_distance

I think it is possible to do this even faster, but i leave it to you to work this out .

Anyway, if you add these up, you'll know what the focusing distance will be.

focusing_distance = object_distance + image_distance

You just need to subtract the total system's lenght to find the WD (Working Distance).
And this you can do by adding the lens' length, with closeup-lens fitted, minus the mount thickness (essentially the bayonet fitting on the lens), plus the flange to sensor distance (Canon EOS: 44.0 mm ), plus image_distance, and subtract all this from the focusing distance. What remains is the distance from front lens to object, or the WD.

In formula:

WD = focusing_distance - (lens_length_with_clos​eup_lens - mount_thickness + 44.0 + image_distance).

Do note that I didn't take the distance between the rear and front nodal plane of the lens into account. This requires experimentation, as I have never seen a list anywhere mentioning those. I reckon it is probably very close anyway.

Kind regards, Wim

P.S.: Another nice article on closeup lenses: http://www.alanwood.ne​t …aphy/close-up-lenses.html

thank you very much for all these explanations and links. Things start to make sense now (though not the math part yet.. got to work on that one more .

Sounds like a +2 diopter lens attached to my 55-250 would do a good job. Canon 500d is a bit expensive, but I saw some Hoya +1, +2 & +4 closeup sets that may be interesting. Will look for review of these now.

thanks again!

cedm wrote in post #6525361
thank you very much for all these explanations and links. Things start to make sense now (though not the math part yet.. got to work on that one more .

Replace each of the long words in the equations with a sigle letter, and it may make it easier to understand .

Glad I could be of help!

Anyway, the Hoya closeup lenses are fine, as are the B+W ones. I've used the latter myself, in the olden days, with film, and before I got a dslr, with the G5.

Worked very well, just that the Canon doublets (250D and 500D) are of better quality.

Kind regards, Wim

I'm back with some samples... This may be useful for other people too.

I borrowed a +3 close up lens (cheap Quantaray, 1 element) from a friend and put it on my nifty fifty. Here's the results:

1. Naked lens, 50mm, F/1.8, closest focusing distance (~45cm):

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